1. Field of the Invention
The present invention relates to an antenna structure and to a method for measuring the azimuth and elevation of an active, signal sending radiosonde.
The present invention is related to atmospheric sounding systems, in which the properties of the atmosphere are measured in-situ by independent, self powered active components typically called radiosondes including a radio transmitter. Typical features for this technique are inactive (non-sending) receiving antennas and the fact that the measuring device (radiosonde) is either lifted or dropped through the space to be measured.
Parameters measured in-situ by sensors of the radiosonde, such as air pressure, temperature and relative humidity, are transmitted through a telemetry link to a receiving station. Other parameters of interest are wind speed and wind direction that can be measured by using navigation aid networks such as GPS or Loran-C, by a primary or secondary radar, or by a passive (non-sending) and independent (no navigation aid networks used) radiotheodolite. Height of the radiosonde can be calculated from the air pressure, temperature and humidity data.
The object of the invention is to determine the azimuth and elevation angles of an active radiosonde in a three dimensional space with a passive (non-sending) antenna structure independent of navigation aid networks. A typical application of the invention is to locate a radiosonde launched into the atmosphere with the help of a balloon filled with hydrogen or helium. Radiosonde azimuth and elevation angles are determined from the received radiosonde signal.
Wind speed and direction can be calculated from consecutive azimuth and elevation angles and height of the radiosonde.
2. Description of Background Art
Prior solutions in the 1680 MHz meteorological frequency band track the radiosonde mechanically both in the azimuth and elevation directions. The disadvantage of this solution is the complicated and expensive mechanical receiving antenna structure.
Another disadvantage of the prior solutions is the disability to attenuate ground reflections enough when the radiosonde signal is received from a low elevation angle.